Pun intended?

As long as workers in the respective country are paid and are not entirely dependend on tips: no.

I also don’t get paid extra money just for doing my job that I am already being paid for. It is so weird and asymmetric that tips are a thing in gastronomy and hospitality. As if these were the only low-wage jobs that can sometimes suck a lot.

If someone is unhappy about their wage, they need to take it up with their boss or organize in a union. It is not my responsibility to pay them.

This is how meta analyses work:
you look at available research, aggregate over it, draw conclusions. It is not unusual that such meta studies even point out that more research is needed.

In fact, it is often helpful to get this ‘more research’ funded.

You guys are still using Google?